Writers of fantasy and science fiction books have special needs. Not only do we have characters to create from scratch, like every novelist, but we have entire worlds to build — not just the verisimilitude of the historical past, but entire planets, spacecraft, or fantastic realms. Our desks are littered with bad sketches of landscapes, terrible character portraits, and far too many scraps of idiosyncratic cosmogenesis.
You know who else has these problems? Dungeon masters.
The world of Dungeons & Dragons and subsequent games created a need for game masters, those referees who control the world of their game for their players, to make maps, create character cards, and so forth. Not surprisingly, there's an ecosystem of software to support this.
A couple of months ago, I invested in most of the software modules from ProFantasy and started playing around. I needed to design a complete secondary world for a new series, The Chained Adept, and it wasn't going to be modeled on Earth at the geology level (although I planned to keep the flora & fauna so that the readers wouldn't need to master an entire ecosystem of vocabulary).
I started by designing a planet, using Fractal Terrains 3. By providing a handful of parameters and tinkering with the results, you can create an infinite number of alien planets.